Webhook: block IPv6 SSRF bypasses

The webhook URL guard's _ip_is_private() only checks a hardcoded
_PRIVATE_NETWORKS list, which misses several addresses that route
internally. validate_webhook_url() therefore ALLOWED:

- http://[::]/                      (IPv6 unspecified, reaches localhost)
- http://[::ffff:127.0.0.1]/        (IPv4-mapped IPv6 loopback = 127.0.0.1)
- http://[::ffff:169.254.169.254]/  (IPv4-mapped cloud metadata endpoint)

The last one is the dangerous case: a webhook pointed at the mapped
169.254.169.254 can pull cloud instance credentials (SSRF -> credential
theft).

Harden _ip_is_private(): first unwrap IPv4-mapped IPv6 to its embedded IPv4
(addr.ipv4_mapped), then reject via the stdlib address properties
(is_private, is_loopback, is_link_local, is_reserved, is_multicast,
is_unspecified) in addition to the existing network list. Public addresses
still pass.

tests/test_webhook_ssrf_resilience.py asserts validate_webhook_url raises
for the three IPv6 bypasses plus 127.0.0.1 and 0.0.0.0, and still accepts a
public IP literal. The IPv6 cases fail before this change.

src/webhook_manager.py

@@ -38,6 +38,20 @@ _PRIVATE_NETWORKS = [
 
 
 def _ip_is_private(addr: ipaddress._BaseAddress) -> bool:
+    # If the address is IPv4-mapped IPv6, extract and evaluate the embedded IPv4
+    if isinstance(addr, ipaddress.IPv6Address) and addr.ipv4_mapped is not None:
+        addr = addr.ipv4_mapped
+
+    if (
+        addr.is_private
+        or addr.is_loopback
+        or addr.is_link_local
+        or addr.is_reserved
+        or addr.is_multicast
+        or addr.is_unspecified
+    ):
+        return True
+
     return any(addr in net for net in _PRIVATE_NETWORKS)
 
 

tests/test_webhook_ssrf_resilience.py

@@ -0,0 +1,28 @@
+import sys
+# conftest.py stubs src.database with a fake module; webhook_manager imports
+# from it, so drop the stub here to load the real module under test.
+if "src.database" in sys.modules:
+    del sys.modules["src.database"]
+
+import pytest
+from src.webhook_manager import validate_webhook_url
+
+
+def test_webhook_url_ssrf_mitigation():
+    # SSRF bypasses that must be rejected, including IPv6 unspecified and
+    # IPv4-mapped IPv6 (loopback + cloud metadata).
+    private_urls = [
+        "http://[::]/",
+        "http://[::ffff:127.0.0.1]/",
+        "http://[::ffff:169.254.169.254]/",
+        "http://127.0.0.1/",
+        "http://0.0.0.0/",
+    ]
+    for url in private_urls:
+        with pytest.raises(ValueError) as exc:
+            validate_webhook_url(url)
+        assert "private/internal addresses" in str(exc.value)
+
+    # A clearly public IP literal must still be accepted.
+    public_url = "http://93.184.216.34/"
+    assert validate_webhook_url(public_url) == public_url